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OsGRDP1 Is a Positive Regulator of Cell Death and Disease Resistance by Activate OsAP25 in Rice

Wensheng Zhao: China Agricultural University

<div>Lesion mimic mutants are valuable materials for unraveling the signaling pathways and molecular mechanisms governing the PCD execution in plants. Here, we identified a dominant mutant <em>spl-D</em> with spontaneous spots-leaf phenotype from T-DNA inserted T1 rice lines. DAB staining showed that intense brown signals were correlated with lesion formation in <em>spl-D</em> leaves, indicating H<sub>2</sub>O<sub>2</sub> accumulation might be responsible for spots emergence. <em>spl-D</em> exhibited enhanced resistances to both <em>M. oryzae</em> and <em>Xoo</em>. Quantitative PCR analysis showed that several defense-related genes known to be involved in SA and JA signaling pathways were constitutively activated in <em>spl-D</em>. TAIL-PCR analysis showed that the T-DNA insertion site locates 495 bp upstream of <em>OsGRDP1</em>. Expression level of <em>OsGRDP1</em> in <em>spl-D</em> was markedly higher than that in the wild type. Moreover, transgenic lines in which <em>OsGRDP1</em> driven by maize ubiquitin promoter exhibited similar phenotypes to <em>spl-D</em>, indicating phenotypes of<em> spl-D</em> were resulted from overexpression of <em>OsGRDP1</em>. OsGRDP1 interacted with an aspartic proteinase OsAP25 in yeast and <em>in vivo</em>. In <em>spl-D</em>, the proteinase activity of OsAP25 was activated, and the lesion formation could be inhibited by pepstain A, an aspartic proteinase inhibitor. In addition, lesion formation of <em>spl-D</em> was accelerated in dark. Taken together, OsGRDP1 is a positive regulator of cell death and disease resistance, which provides a new clue to elucidate the mechanism of lesion formation.</div>